The field of this invention relates to welding equipment and more particularly to a mounting fixture for precisely locating of an automatic welding apparatus in order to obtin the highest quality weld.
In certain applications, there are manufactured parts that require internal welding. An example of such a part is a heat exchanger which is used in nuclear applications. This heat exchanger is constructed of a mass of closely spaced metallic tubes. These tubes terminate at one end at a metal sheet. Each tube connects with appropriate openings formed within the metal sheet. The point of connection of each tube to the sheet is precisely determined. The tubes may or may not be evenly spaced apart. The tubes are arranged in rows, with there normally not being the same number of tubes within each row. The location of the tubes within each row is determined from a drawing. Each tube must then be welded to the sheet, with the weld being performed within each opening in the sheet.
In order to achieve a high quality weld, an automatic welding head is utilized. Manual welding is not feasible, since there will normally be several hundred in number of tubes connected to a single sheet. The welding electrode of the automatic welding head must be centered at the precise center point within each opening during the performing of the weld. It has been common to mount the welding head onto a separate mounting strip. There is prefabricated a separate mounting strip for each horizontal row of openings. Each mounting strip includes a series of notches, with each notch to correspond to the center of an opening. Therefore, allegedly, the attaching of the welding head onto the strip at a particular notch is to result in the welding electrode being located at the exact center point of an opening. Therefore, rotation of the welding head will be precisely concentric with the wall of the opening. This means that the welding electrode will continuously remain at the same distance from the wall of the opening as the welding electrode is moved three hundred and sixty degrees around the wall of the opening during the welding of the tube to the sheet. It is to be noted that the diameter of each tube is identical so that the welding head need only be initially preset for a particular diameter.
Each notched strip is manufacturered from a drawing. The location of each opening within the sheet (as previously mentioned) is also determined from a drawing. If there are absolutely no errors in the locating of each opening and the locating of each notch, then the position of the welding head at each notch will result in a precisely centered welding electrode within an opening. However, errors are known to occur and it only takes an error in the matter of a few thousandths of an inch to result in the welding electrode not being accurately centered within an an opening. Also, frequently when an error occurs within one opening, the subsequent openings in a given row are subjected to the same error. An error of just a few thousands of an inch will result in the producing of a poor quality weld within a opening.